What colors might an alien's blood be?

[pincushionman]

Yeeeah, now we've managed to boil it down to philosophy …

That's because it IS philosophy!

[smjjames]

Any color is possible. On Earth we have this, assuming I remembered everything correctly:

- Red in humans

- Clear in antarctic fish

- Light green in arthropods

- And some creature has blue, but I forgot which.

You're probably thinking of horseshoe crabs.

[NuclearNut]

Unless they are robots they need some circulation fluid to feed the cells.

Its the simplest solution and therefor the most probable.

Heck, even if it is a robot it needs circulation to cool it's processors. Either way it is going to have some sort of fluid in it, weather for cooling, heating, or transporting chemicals.

[Cirocco]

okay, having thought a bit more on this question, here's my two cents that are actually on topic and not "it's all a matter of philosophy"

I think the question that is actually being asked here is "what color could blood be?" considering blood to be a fluid used by a life form close to what we consider life in its circulatory system.

the answer is probably something along the lines of "almost any (uniform) color"

As stated already in this thread: blood gets its red color from the iron in hemoglobin. The iron's color also varies with its oxidation state. While de-oxygenated blood is not actually blue as so many high-school diagrams would have you believe, it does in fact differ in color from oxygenated blood (it's a lot darker if my memory serves me correctly).

let's assume that the deciding factor in (alien) blood color is also the oxidation state of the metals in their organo-metal enzymes (also assuming they use those). Let's also assume that they don't necessarily use oxygen as part of their energy cycle but that other atoms or even small molecules are also possible. This means that just about any transition metal is on the table. And transition metals can have a LOT of colors depending on their oxydation state.

a few examples:

white, silvery-grey, metallic (titanium)

red or black (iron)

grey, deep blue, black, yellow/orange-y (vanadium)

blue or green (copper)

black or colorless (ruthenium)

etc...

there's a LOT of colors out there when it comes to transition metals. And it gets even more funky if you drop the requirement for that.

Edited October 21, 2015 by Cirocco
Vanadium is funky...

[RuBisCO]

Way back in my bachelors I once did a report on this for biochemistry and put little parts of it years ago into Wikipedia. I'm partial to Hemerythrin, its pink when oxygenated and clear when not, it uses twice a much iron per oxygen molecule bond as our blood but its impervious to CO and SH2 poisoning.

Hemocyanin is copper based and is cool blue.

Vanabin based blood though hypothetically could carry oxygen, the is no actual evidence for it and the reason why some organism have vanadium in their blood is unknown. In theory vanadium could support multiple oxidation states and shift in color from green to purple to orange.

[FungusForge]

I look away for 2 minutes...

Gosh you Science Labs guys are interesting. And a great deal more entertaining than Google.

[Cirocco]

I look away for 2 minutes...

Gosh you Science Labs guys are interesting. And a great deal more entertaining than Google.

credit for that doesn't go to us, it goes to SCIENCE!!!!